Types of Protein Secondary Structures and Their Biological Roles
Before understanding how the proteins are classified on the basis of the secondary structure of protein, it is essential to know why proteins are so important. Nearly every single function in the organisms is a result of the proteins. These components account for about 50% of the entire cell mass and have a pivotal role to play in every single process of the body.
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There are different types of proteins that play different roles in speeding up the chemical reactions, providing defense, storage, movement of cells and communication, and structural support in organisms. Human beings have thousands of different proteins existing in their bodies at any particular time. Every single one of these proteins has its very own function and structure.
Classifying Proteins According to the Secondary Structure
Every protein has its description from the structure that it has. These structures are primary structure, secondary structure, tertiary structure, and quaternary structure. To explain it in brief, the primary structure focuses on the linear chains consisting of amino acids.
The secondary structure consists of different regions stabilized due to the presence of hydrogen bonds. The tertiary structure represents the 3-D protein shape determined by all the stabilized regions due to the interactions of side chains. The Quaternary structure is an association created by polypeptides. In this article, students will get to focus on the secondary structure of protein example.
What is the Secondary Structure of a Protein?
The secondary structure of protein refers to the three-dimensional form associated with the local segments that are present in proteins. The two common elements in the classification of the secondary structure of protein include beta-sheets and alpha-helices. Although beta turns and omega loops are occurrences of the secondary structure too, they are not very common. The elements of secondary structure are spontaneously formed as a type of intermediate before the protein is folded into the three-dimensional structure.
The hydrogen bonds formed in the secondary structure between the carboxyl oxygen and amino hydrogen atoms help describe the structure perfectly. These bonds occur on the backbone of the polypeptides. The secondary structure might be alternatively defined on the basis of some regular patterns seen in the backbone dihedral angles.
This secondary structure of protein diagram will help explain the topic in detail.
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Difference Between Primary and Secondary Structure of Protein
Here is the difference between primary and secondary structure of protein.
There are two different structures included in the secondary structure. Alpha helix and beta-pleated sheets are the most commonly occurring elements. Since the polypeptide chain backbone is constantly folding due to the presence of hydrogen bonding, the structure is created. There are certain segments belonging to the chain of proteins that might have their very own fold locally. This enables the structure to become much simpler. Such local folds are named secondary elements and result in the formation of the secondary structure of proteins.
Conclusion
The secondary structure of protein takes the next level upwards from the protein’s primary structure. It is also the regular folding of different regions into certain specific structural patterns that exist within a single polypeptide chain. The secondary structures’ primary function is to hold the hydrogen bonds together that are created between the amide hydrogen and the carbonyl oxygen in the peptide bonds.
FAQs on Secondary Structure of Protein Explained
1. What is the secondary structure of a protein as per the CBSE syllabus for 2025-26?
The secondary structure of a protein refers to the local, repetitive coiling or folding of the polypeptide backbone. It is the second level of protein organisation, arising from the primary structure. This structure is not random but forms specific, stable arrangements, primarily due to hydrogen bonding between atoms in the polypeptide backbone, not the side chains.
2. What are the two main types of secondary structures found in proteins?
The two most common types of secondary structures in proteins are:
Alpha-helix (α-helix): This is a right-handed coiled or spiral conformation where every backbone N-H group donates a hydrogen bond to the C=O group of the amino acid four residues earlier.
Beta-pleated sheet (β-sheet): This structure consists of polypeptide chains linked laterally by hydrogen bonds. The chains can run in the same direction (parallel) or in opposite directions (antiparallel), forming a folded, sheet-like structure.
3. How does the secondary structure of a protein differ from its primary structure?
The key difference lies in their dimensionality and the bonds that define them. The primary structure is a one-dimensional, linear sequence of amino acids linked by peptide bonds. In contrast, the secondary structure is a three-dimensional arrangement (like a helix or sheet) formed by the folding of this linear chain, which is stabilised by hydrogen bonds between the backbone atoms.
4. What is the fundamental force responsible for stabilising a protein's secondary structure?
The fundamental force responsible for stabilising the secondary structure is the hydrogen bond. These bonds form between the carbonyl oxygen (C=O) of one peptide bond and the amide hydrogen (N-H) of another. While a single hydrogen bond is relatively weak, the presence of many such bonds throughout the structure provides the collective strength needed to hold the α-helices and β-sheets in their specific shapes.
5. How does the amino acid sequence in the primary structure influence the formation of secondary structures?
The sequence of amino acids is critical because the properties of their side chains (R-groups) dictate which secondary structure is more likely to form. For instance:
Amino acids with small or uncharged side chains often favour the formation of an α-helix.
Amino acids like proline, known as a 'helix breaker', disrupt the regular helical structure.
Sequences with bulky side chains or those that form a pattern of alternating properties may favour the formation of β-sheets.
6. Can you give an example of a protein that is rich in a specific secondary structure?
Yes, a classic example is keratin, the structural protein found in hair, skin, and nails. Keratin is predominantly composed of alpha-helices, which gives it its fibrous and strong characteristics. Another example is fibroin, the protein in silk, which is rich in beta-pleated sheets, contributing to its strength and flexibility.
7. Why is the secondary structure important for the final function of a protein?
The secondary structure is a crucial intermediate step in protein folding. It provides a defined, stable framework that folds further to create the complex tertiary structure. The specific arrangement of α-helices and β-sheets is essential for forming the protein's final three-dimensional shape, which includes critical features like active sites in enzymes or binding domains. Without the correct secondary structure, a protein cannot achieve its final functional form.
8. Why do alpha-helices form a coil while beta-pleated sheets form a flat, folded structure?
The difference in shape is due to the pattern of hydrogen bonding. In an alpha-helix, the hydrogen bonds form between amino acids that are close together in the linear sequence (specifically, every fourth amino acid), causing the polypeptide chain to twist into a tight, regular coil. In a beta-pleated sheet, the hydrogen bonds form between segments of the chain that lie side-by-side, linking different parts of the polypeptide together and creating a more extended, sheet-like arrangement.
